This invention relates to a method for controlling an engine or more in particular to a system for stably controlling the fuel injection amount, ignition timing or the like using an electronic control circuit even in a transient condition.
In a well-known control system for controlling the ignition timing or intermittent fuel injection using an electronic circuit, the flow rate of air taken into the engine per unit time and the rotational speed of the engine are detected, and in response to such values, the control amount is calculated. Such a calculation is repeated at a predetermined frequency or in synchronism with engine rotation, so that data on the air flow rate and rotational speed are detected and used within a short time in synchronism with the calculation. In order to detect the air flow rate, a rotational signal in the form of an electrical output from an air amount sensor arranged in the intake manifold or an electrical signal obtained from a rotary member rotated in synchronism with the crank shaft or cam shaft is used.
In a well-known air amount sensor comprising a sluice plate arranged in the intake manifold upstream of the throttle, in which the opening of the sluice plate changing with the air flow rate is converted into an air signal by a potentiometer, the motion of the sluice fails to correspond to the actual change in air flow rate in a transient condition where the driver suddenly opens or closes the throttle. As a result, the fuel injection amount or ignition timing calculated from this air flow rate signal develops an error temporarily, thus causing a vehicle vibration uncomfortable to the driver sometimes. More specifically, when the throttle is suddenly opened, the engine demands the fuel being increased through a kind of the primary delay system while the output of the air amount sensor exhibits a response characteristic like that of the secondary delay system. The additional fuel to be injected in response to such an operation of the throttle is short of or exceeds in amount the actual fuel requirement.
In the case where the engine is driven with the throttle full open and at low speed, the secondary vibration system is formed sometimes by the engine, the driving system and the vehicle system with the rotational speed as a parameter, thus starting a vibration at a natural frequency under certain conditions. In such a case, the fuel injection amount and ignition timing calculated from the original rotational speed develop an error, so that a change in rotation is promoted, thus often giving rise to a vehicle vibration uncomfortable to the driver continuously.